Process for dismantling an irradiated component of a nuclear reactor by the cutting of its wall

Abstract

The irradiated component (1) comprises at least one tubular wall with its axis vertical and fastened inside a well (2) in a concrete structure (3). The connecting elements between the concrete structure (3) and the component (1) are destroyed, the component (1) is displaced in successive steps in the vertical direction along its axis on the inside of the well (2), and the wall of the component is cut, so as to obtain blocks (26) of irradiated material of the wall, at the upper level of the well (2) of the concrete structure (3) after each displacement of the component (1). The cut blocks (26) are disposed of for the purpose of elimination or storage. The displacement of the component can be obtained by a pull or push on its lower bottom.

We claim: 
     
       1. A process for dismantling an irradiated component of a nuclear reactor, said component comprising at least one tubular wall arranged with its axis in a vertical direction, connected by connecting elements and fastened inside a well made in a concrete structure, said process comprising the steps of: (a) severing connecting elements between said concrete structure and said component;   (b) vertically displacing said component in successive steps along its axis on an inside of said well;   (c) cutting said wall of said component over a height corresponding substantially to a distance of vertical displacement, so as to obtain blocks of irradiated material of said wall, at an upper level of said well after displacement of said component;   (d) disposing of the cut blocks for elimination or storage; and   (e) cutting said component in successive steps separated by a displacement in the vertical direction.   
     
     
       2. Process according to claim 1, wherein cutting of said wall of said component to obtain blocks of irradiated material is carried out by a cutout in a substantially horizontal direction followed by cutouts in a substantially vertical direction. 
     
     
       3. Process according to claim 2, wherein a cut in a substantially horizontal direction is made along a slightly inclined helix having an axis coincident with the axis of said component, and is followed by a cutting operation in a direction slightly inclined to the vertical. 
     
     
       4. Process according to claim 2, wherein the cut in a substantially horizontal direction is made in a cross-sectional plane of said component and is followed by cutting operations in the vertical direction. 
     
     
       5. Process according to claim 1, wherein said component is rotated about its axis at the end of some cutting operations. 
     
     
       6. Process according to claim 1, wherein vertical displacement of said component comprises the successive steps of (a) positioning first means for raising said component under a lower part of said component and so as to bear on a stationary support resting on said concrete structure in the vicinity of the bottom of said vessel well;   (b) lifting said component by a push of said first raising means on said lower part of said component;   (c) introducing a first modular supporting element between said lower part of said component and said stationary support on which the modular element comes to bear;   (d) actuating said first raising means in a direction opposite to the lifting direction, in order to bring said lower part of said component to bear on said first modular element; and, for each subsequent successive displacement step of said component:   (e) executing a unit lift of said component over a specific vertical distance by second raising means bearing on said stationary support, in engagement with a modular supporting element interposed between said component and said stationary support and resting on said stationary support before the unit lift of said component;   (f) introducing a modular supporting element, the height of which is smaller than the vertical distance of unit lift of said component, between said modular element with which said second raising means interact and said stationary support; and   (g) actuating said second raising means in a direction opposite to the lifting direction, in order to bring said component to bear on said stationary support by means of the superposed modular elements.   
     
     
       7. Process according to claim 6, wherein said component is a nuclear-reactor vessel resting, by means of supporting feet fastened to a vessel bottom, on a supporting ring resting on said concrete structure of said reactor, and comprising the steps of: (a) cutting cutouts in said supporting ring vertically in line with at least some of said supporting feet;   (b) arranging a lifting jack in each of said cutouts made vertically in line with a supporting foot;   (c) raising said vessel over a specific vertical lifting distance by use of some of said jacks coming to bear on corresponding supporting feet, and, after lifting of said vessel has been carried out, placing wedging pieces under those of said jacks which have not been used for lifting, so as to bring said jacks to bear on corresponding supporting feet; and   (d) lifting said vessel by successive passes comprising lifting by some of said jacks and wedging of jacks not used for lifting.   
     
     
       8. Process according to claim 7, comprising cutting said supporting ring in order to provide cutout zones aligned two by two, and introducing into said aligned cutout zones at least two sections resting on said fixed concrete structure of said reactor and intended for forming part of said stationary support vertically aligned with said bottom of said vessel and a transfer track for bringing said modular supporting elements vertically into alignment with said bottom of said vessel. 
     
     
       9. Process according to claim 8, wherein said second raising means bear on said supporting ring for the purpose of executing a unit lift of said vessel. 
     
     
       10. Process according to claim 6, where, prior to the unit lift of said vessel, said second raising means are assembled, by means of removable assembly elements, together with said modular supporting element resting on said stationary support before the unit lift of said component. 
     
     
       11. Process according to any one of claims 6 to 10, comprising fastening to said lower part of said component a support, by means of which said lower part of said component is brought to bear on said modular supporting elements.